1. Field of the Invention
The present invention relates to an image display apparatus equipped with a digital interface such as Digital Visual Interface (DVI) or High-Definition Multimedia Interface (HDMI, registered trademark), and particularly, to the adjustment of a setup level and a dynamic range of an input digital video signal.
2. Description of the Related Art
Since individual local broadcast standards specify their setup levels of the analog video signal, conventional image display apparatuses perform a setup cancel operation uniquely defined in each region. The term “setup level” means a difference between the pedestal level and the black level of the video signal. In the United States, the setup-level is 7.5%, and a setup cancel operation of 7.5% is carried out, for instance. In Japan, the setup level is 0%, and a setup cancel operation of 0% is carried out. When a setup cancel operation is carried out for a video signal with a setup level added, the lower limit of quantization of the AD converter is shifted by an amount of the setup cancel. Refer to Japanese Patent Kokai (Laid-open) Publication No. 2001-339621 (pages 4 to 5 and FIG. 1), for instance.
Digital interfaces such as DVI and HDMI (registered trademark) incorporated in digital versatile disk (DVD) players and set-top boxes (STB) are becoming pervasive. The RGB signals output from the digital interfaces are divided into two types by dynamic range: a full range and a limited range. The dynamic range to be used is determined by each apparatus, irrespective of the region, and both dynamic ranges are used in a single region. With a full range 8-bit video signal, all of the 256 values (i.e., quantization bit number) formed by 8 bits are assigned to the gray levels respectively, where a level 0 is black and a level 255 is white. With a limited range video signal, a level 16 is black, and a level 235 is white, and part of the 8-bit values are used.
If a limited range video signal is input to a conventional image display apparatus supporting the full range, problems known as “dull black” (increase in brightness of black) and “dull white” (decrease in brightness of white) occur. If a full range video signal is input to a conventional image display apparatus supporting the limited range, problems known as “black crushing” (loss of grayscale details in a dark area) and “white crushing” (loss of grayscale details in a light area) occur.